Abstract:
The rate of discharge through the stray electrolytic capacitor between the pipe and the
remote earth is to be considered as the corrosion current. The electrochemical properties
of the soil, which are the soil resistivity of the soil volume, the relative permittivity of
the soil layer around the pipe and the chemical properties which could be considered as
the pH of the soil film layer around the pipe, are affected directly by the humidity
change. When considering the room temperature and by neglecting the effect of CO2
content in the soil, these values of the electrochemical properties of any soil returns
back to its initial conditions after soil dryness to its initial condition. This means that
corrosion rate will also be changed during the humidity change around the pipe
segment. So, when considering the fact that the pipeline will not be changed or replaced
and the surrounding medium around it will not be changed or replaced by another kind
of soil, then the behavior of the electrical parameters (stray electrolytic capacitance,
stray potential, surface created charge) of the pipe-soil-earth system will act as a print of
this combination of this pipe and this soil. This paper recalculates the general form of
the equations of the electric parameters and obtains the print curves & constants at
natural condition with and without applying cathodic protection system in terms of the
electrochemical properties around the pipe. The average error reduced to be less than ±
5%. This will help to study both the corrosion problem and cathodic protection by an
electric concept with an electric analogue circuit which is the aim of this study.